This invention relates to video security systems and a method for detecting the presence of an intruder into a scene; and more particularly to the discernment of an intruder based upon sensed surface differences which occur within the scene rather than lighting changes which may occur therewithin.
In co-pending, co-assigned U.S. patent application Ser. No. 08/772,595 there is described a video security system and method by which a reference scene is established for comparison with later images of the same scene. These comparisons are made to determine if there are any differences between the scenes. If there are marked differences between the contents of the two images, this is interpreted as an intrusion of some kind having occurred within the scene. A primary function of the system and the method it employs is to identify and classify intruders into a scene and only notify security personnel in the event an intruder is human. All other anomalies which produce a difference between the two images are identified as false alarms for which no notification is given. In the security system as described in co-pending application Ser. No. 08/772,595, the possibility of false alarms caused by lighting changes within a scene, whether natural or manmade, global or local, is addressed. As discussed therein, the differences between the reference scene and a later scene resulting from lighting effects can be now be identified so that no false alarm results from them. However, there are other potential causes of false alarms which also must be recognized. The video security system and image processing methodology as described herein recognizes anomalies resulting from these other causes so these, too, can be accounted for.
Previous attempts have made to provide a reliable security system to detect the presence of a person in a scene using a video system. In U.S. Pat. No. 4,697,097, for example, a reference image of a scene is compared with a subsequent image to detect the presence of an object (an anomaly which may or may not be caused by a human intruder) with the image then being transmitted to another location for review by a human. U.S. Pat. No. 4,257,063, teaches comparing a video line (not a whole image) from a camera with the same video line produced at an earlier time to detect the presence of a human. No compensation is made for light changes, nor is an attempt made to recognize the contents of the image as being a human intruder. Similarly, U.S. Pat. No. 4,161,750, teaches that changes in the average value of a video line can be used to detect the presence of an anomalous object. While this art generally teaches some type of detection, it does not address the use of image processing as an automatic recognition stage to prevent false alarms, nor the use of image processing to distinguish differences between a reference image and a later image for effects such as noise, aliasing, repetitious movements, etc. which can also produce false alarms. This applications describes both recognition of objects due to surface differences which are present between the reference image and a later image against which it is compared, as well as identifying these other sources of potential false alarms.